Disclosed herein are nano-sized composites and a method for making toner particles or developers using these composites. Each nano-sized composite may contain a polymer modified clay that may include, for example, polystyrene, polyester and the like. The nano-sized composites may have clay platelets orientated in an intercalated, exfoliated or tactoid structure or a dispersion of clay particles within a polymer matrix.
The nano-sized composites may be incorporated into a bulk or a binder of a toner, such as a conventional toner or an emulsion aggregation toner. Incorporating the nano-sized composites into toner particles improves relative humidity (hereinafter “RH”) sensitivity of the toner and charging performance in low and/or high humidity conditions. The nano-sized composites within the toner particles may be advantageous in improving one or more of elastic modulus, reducing water vapour permeability or additive impaction, raising blocking temperature and vinyl document offset.
Toners, such as emulsion aggregation (hereinafter “EA”) toners, are excellent toners to use in forming print and/or xerographic images in that the toners can be made to have uniform sizes and in that the toners are environmentally friendly. Common types of emulsion aggregation toners include emulsion aggregation toners that are acrylate resin based or that are polyester resin based toner particles.
Emulsion aggregation techniques typically involve the formation of an emulsion latex of the resin particles, which particles may be nano-sized from, for example, about 5 to about 500 nanometers in diameter, by heating the resin, optionally with solvent if needed, in water, or by making a latex in water using emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally also with additional resin, is separately formed. The colorant dispersion is added to the emulsion latex mixture, and the mixture is aggregated, for example at an elevated temperature, optionally with addition of an aggregating agent or completing agent, to form aggregated toner particles. The aggregated toner particles are optionally further heated to enable coalescence and fusing, thereby achieving aggregated, fused toner particles.
Digital printing images are formed using toner compositions with a printer. The toner compositions typically include small powders having small toner sized particles with a controlled particle shape. However, small toner sized particles often cause performance difficulties because of the physics associated with the small toner sized particles. As a result, external surface additives, such as metal oxides, are added to the small toner sized particles to control charging stability, toner flow, toner adhesion and/or blocking. However, with time and damage from developing housings, the toner flow and toner adhesion of the small toner sized particles may change and the small toner sized particles can block, which affects image quality.
Additionally, charging with metal oxide additives may often cause the small toner sized particles to exhibit a higher relative humidity sensitivity (hereinafter “RH”) than desired, and thus may not perform well in all humidities. It is desirable that the toner compositions be functional under all environmental conditions to enable good image quality of the digital printing images from the printer. In other words, it is desirable for the developers to function both at low humidity such as a 10% RH/15° C. relative humidity (denoted herein as C-zone) and at high humidity such as at 85% RH/28° C. relative humidity (denoted herein as A-zone).
Thus, the physics of small powders, such as small toner sized particles or EA toner particles, can cause several problems for developers that hinder the ability to form high quality images.
One solution to these problems has been to add external surface additives to the toner compositions. Such external surface additives may include metal oxides to control developer charging stability, toner flow, toner adhesion, transfer and blocking. However, with time and abuse from the developing housings, developer stability, toner flow and toner adhesion change and the toner may block, which may affect image quality. Additionally, charging small toner sized particles with metal oxide additives often provides higher RH sensitivity than desired.
Additive impaction of (external surface additives being embedded into toner) which leads to charge, flow and adhesion degradation, may be improved by increasing resin elasticity by modifying polymer properties of the small toner sized particles. To modify the polymer properties, a gel or a second higher molecular weight (hereinafter “Mw”) distribution polymer may be added to the toner or the small toner sized particles. Thus, blocking may be improved by increasing a glass transition temperature (hereinafter “Tg”) of the toner compositions. However, the gel or the second higher Mw distribution polymer may cause an increase in the minimum fusing temperature (hereinafter MFT), which is disadvantageous because a higher fuser roll temperature and also higher pressure will be needed, which may cause a decrease in the life of fusing rolls system.
The RH sensitivity for the toner compositions may be improved by adding a charge control agent to the bulk of the toner formed from the small toner sized particles. However, addition of a charge control agent (CCA) to the bulk of the toner is often unsuccessful for toners because the CCA often increases toner charging only in C-zone conditions and not in A-zone conditions, leading to higher RH sensitivity.
Thus, a need exists for better methods to improve RH sensitivity and charging performance of toner particles while avoiding problems associated with the inclusion of external surface additives and the like.